Cutting tool equipped with a state indicator

ABSTRACT

A cutting tool equipped with a tool state detector which comprises temperature sensors and conductors which are placed on the tool. The invention is characterized in that two or more temperature sensors (10-13) are placed on the tool (1) at mutually different distances from the tool cutting edge (3), so that the temperature distribution in the tool (1), at least at the cutting edge (3) and its immediate vicinity, can be established from electric signal emitted by the sensors (10-13), and that at least some of the sensors are so placed that one or more of the sensors will be worn away in successive sequence as the tool (1) wears. The temperature sensors (10-13) are preferably thermoelements.

This application is a continuation-in-part of application Ser. No.07/344,453, filed Apr. 28, 1989, now U.S. Pat. No. 4,945,770, issuedAug. 7, 1990, which is a continuation of Ser. No. 099,318 filed Aug. 11,1987 now abandoned.

The present invention relates to a cutting tool equipped with a toolstate indicator, and more specifically to a state indicator formeasuring tool temperature and tool wear.

BACKGROUND OF THE INVENTION

The cost of a machining operation which requires the use of cuttingtools is highly dependent on the wear rate of the tool. Consequently,attempts have been made in the past to measure tool wear directly, andto assess the useful length of life of a tool on the basis of tool wear,primarily on the basis of chamfer wear on the relief or clearance sideof the tool. An experienced machine operator will be able to judgeroughly with the naked eye whether or not the tool needs to be changed.

In present times automatization has progressed to such lengths thatthere is often no operator available, and consequently attempts havebeen made, for instance, to work with automated wear measuring methodswith the use of image processing systems, which is an expensive and slowsolution to the problem. It is necessary with such machines to haltmachining work while the measurements are being taken. Attempts havealso been made to measure tool wear indirectly, by measuring prevailingcutting forces, the changes in which forces are contingent on wear onthe tool. The relationships, however, are not always specific andconsequently the method is not reliable.

A third method involves measuring cutting temperatures, e.g. with theaid of a thermoelement inserted into a bore drilled in the tool. Thisresults in mechanical weakening of the tool, however, and it is verydifficult to drill holes in the extremely hard material from which suchtools are made and to position the holes with precision. Tooltemperatures are measured in on attempt to calculate the temperature ofthe cutting tool in the critical zone around the cutting edge--thecontact surfaces between tool and chip or swarf and tools and workpiecerespectively.

For mechanical strength reasons, it is necessary to place thethermoelement at a relatively long distance from the actual cutting edgeand the temperatures measured will differ radically from the temperaturewhich actually prevails at the contact surface and which determines thewear rate of the tool.

CROSS REFERENCE TO RELATED APPLICATION

It is disclosed in Swedish Patent Specification 8403609-4 dated Apr. 7,1988 and from Swedish Patent Application 8403609-4 filed Jul. 6, 1984and published on Jan. 7, 1986 under Publication No. 452,911, that athermoelement and/or thermistor can be configured, for instance, withthe aid of thin film techniques so as to measure the temperature of aspot or punctiform location on a tool or some other mechanicalcomponent.

Applicants' U.S. Pat. No. 4,945,770 dated Aug. 7, 1990 corresponds inits disclosure with Swedish Patent No. 8403609-4. The U.S. applicationSer. No. 344,453 was filed 99,318, dated Aug. 11, 1987 (abandoned), andhas a priority filing date of Jan. 2, 1986 based on PCT applicationPCT/SE86/00001 (Published as WO87/04236 on Jul. 16, 1987).

The aforesaid Swedish Patent Specification (U.S. Pat. No. 4,945,770)also discloses that tool wear can be measured successively with the aidof a plurality of conductors connected to the cutting edge, since theresistances in the conductors will change gradually and abruptly,depending on the extent to which the conductors are worn away.

SUMMARY OF THE INVENTION

It is highly desirable to be able to control a cutting process in amanner which will enable the process to be effected under optimumconditions with respect to cutting speed, feed and tool wear. However,the cutting properties of the machined material will vary from workpieceto workpiece, and even within one and the same workpiece. Consequently,when employing known techniques it is necessary to choose relevantcutting data conservatively, so that the tools are able to withstand themost difficult loading situations, which means that it is oftennecessary to work at excessively low cutting speeds or feeds.

It is also desired to avoid the occurrence of tool catastrophes, withthe tool in engagement with the workpiece.

This desire is particularly manifest in the case of large and/orexpensive workpieces.

The present invention fulfills the above mentioned objectives. It ispossible with the aid of the present invention to calculate or establishthe temperature distribution in a cutting tool and to obtain informationrelating to the extent of tool wear at any given moment in time.

This will enable an optimum cutting speed or feed to be selected at anygiven moment.

It is also possible by means of the invention to obtain continuouslyinformation which relates to the distribution of temperature in the tooland to the extent of wear thereon, and to calculate on the basis of thisinformation cutting data or criteria which will enable work to becompleted on the workpiece being machined without risk of a toolcatastrophe. Of course, it is necessary in this respect to haveavailable experimental data obtained from earlier machining or cuttingoperations. Such data however, can be accumulated readily while applyingthe present invention.

The present invention thus relates to a cutting tool equipped with atool state indicator. The state indicator comprises temperature sensorsand a plurality of conductors applied to the tool, and is characterizedin that two or more temperature sensors are placed on the cutting toolat mutually different distances from the cutting edge of the tool, so asto enable the temperature distribution in the cutting tool, at least atthe cutting edge thereof and in the immediate proximity of the edge, tobe calculated from electric signals transmitted from the temperaturesensors; and in that at least some of the sensors are so placed as to beworn away in sequence and progressively as the tool wears.

The invention will now be described in more detail with reference to anexemplifying embodiment thereof illustrated in the accompanyingdrawings, in which

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side view of a flat indexable insert;

FIG. 2 illustrates the invention as applied to an indexable insert seenfrom the right in FIG. 1;

FIG. 3 is a bottom view of the indexable insert illustrated in FIG. 2.

FIGS. 4 and 6 are respective cross-sectional views taken through anouter part of the flat indexable insert; FIGS. 5 and 7 are views of anindexable insert corresponding to the view of FIG. 2 and illustratingalternative embodiments of the invention;

FIG. 8 illustrates the chip breaking side of a triangular indexableinsert; and

FIG. 9 is a dotted line schematic block diagram showing a tool holderwith contacts, which correlate with those on the insert shown in FIG. 3,and conductors from the contacts to a signal processor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate a flat insert 1. FIG. 1 shows the insert platefrom one side and illustrates a clearance angle 2 of about 6° to theright and to the left end surfaces 28 of insert plate 1 and extendingdownwards from the cutting edge 3. An indexable insert of this kind willinitially wear so as to form a chamfer wear surface 6 (FIG. 2) having awidth (H) of less than 0.1 mm. The arrows 4 illustrate the direction inwhich the material is advanced relative to the insert 1. The arrow 5shows the transport direction of the chips. Such indexable inserts arevery well known per se and can be made of various materials, such ashardmetal, ceramics, high-speed steel and other hard allows. They canalso incorporate diamonds or boron nitrides, to greater and lesserextents.

A wear protective layer is normally applied to the base metal of theinsert. This wear protective layer or antiwear layer, will preferablycomprise TiN, TiC or Al₂ O₃. Another suitable protective covering isboron nitride. The wear protective layer will have a thickness, forinstance, of 0.5-50 microns.

As will be understood, the present invention relates to cutting tools ingeneral and is thus not restricted to the cutting tools illustrated inthe drawing, which solely illustrates examples of how the presentinvention may be applied. The cutting tools are equipped with tool stateindicators comprising temperature sensors and having conductors whichare mounted on the cutting tools concerned.

The conductors and/or the temperature sensors can be mounted on the toolso as to form therewith an atomically integrated unit, e.g. with the aidof PVD or CVD techniques or a photo-chemical method.

Alternatively, the conductors and/or sensors can be applied with the aidof a printing method and a subsequent sintering process. It is thuspossible to use both a thick film technique and a thin film technique.Depending on the method used, the thicknesses of the conductors andtemperature sensors may vary, for instance from 0.1 micron to 5.0microns.

According to the invention, two, three or four temperature sensors 10-13are placed on the cutting tool 1 at mutually different distances fromthe cutting edge 3, so that the temperature distribution in the tool, atleast at the cutting edge thereof and in the near vicinity of the edge,can be calculated from electric signals transmitted from the temperaturesensors. Also in accordance with the invention, at least a some of thesensors are so placed that one or more sensors will be worn away insuccessive sequence as the tool wears.

According to one preferred embodiment the temperature sensors have theform of thermoelements.

The width of the chamfer wear surface varies from an initial value ofzero mm (0 mm) to a given width value of, e.g., up to 0.7 mm, at whichthe cutting tool is considered to be worn out.

According to one preferred embodiment, two or more thermoelements areplaced on the clearance or relief surface 28 of the cutting tool at adistance from the cutting edge such as to be worn away with increasingwear of the wear surface of the tool.

Preferably a plurality of thermoelements are placed on the clearancesurface, with at least one thermoelement placed at a greater distancefrom the cutting edge than the dimension corresponded by the greatestintended width of the chamfer wear surface when the tool is consideredto be worn out.

The cutting tools may be made of both electrically conductive andelectrically insulating material.

When the cutting tool is made of an electrically conductive material,the tool is provided with an insulating layer, e.g. a layer of Al₂ O₃onto which electrical conductors are applied. The layer may suitablyhave a thickness of 1 to 10 microns.

In the illustrated example of FIG. 2, a number of thermoelements 10-13are placed at mutually different distances from the cutting edge 3, withthe thermoelement 10 located nearest the edge being placed adjacent toor immediately beneath an initially obtained chamber wear surface 6. By"initially" is meant after a short time of use, for instance after aboutone minute of use.

Accordingly to a first embodiment of the invention, see FIG. 4, aconductor 20 for each thermoelements is applied to an electricallyinsulating layer 22 provided on the tool base material 21. Formed in theinsulating layer 22 is a hole 23, in which one end 24 of the conductor20 is brought into contact with the base material, to form athermocouple. In this case, the cold solder location (not shown) foreach thermocouple is placed at a distance from the tool, e.g. on thetool holder.

Many materials in combination form thermocouples which generate anelectric voltage in accordance with the well known thermoelementprinciple, Seeveck effect. The invention is not limited to anyparticular combination of dissimilar materials. For instance, when thetool base metal is hardmetal, the conductor 20, 24 may consist of ironor platinum for example, whereas when said base metal is high-speedsteel, the conductors 20, 24 may consist of gold.

The aforesaid hole 23 may, for instance, be formed with the aid of alaser, prior to applying respective conductors 20 to the cutting tool.Subsequent to applying the conductors 20, the cutting tool is preferablycoated with an electrically insulating and wear protective layer 25,suitably Al₂ O₃.

This first embodiment is illustrated in FIGS. 2 and 3, in which only oneconductor 20 extends to respective thermocouples.

The contact plates 26 of each one of the respective conductors 20 may beplaced on the undersurface 27 of the tool, as illustrated in FIG. 3, ormay be placed on the clearance side 28 of the tool, as illustrated witha broken line in FIG. 2 for one of the conductors 20. The tool holderTH, seen in FIG. 9 has arranged thereon electric contact devices 76which are intended to lie against associated contact plates 26 ofrespective conductors 20. The contact plates 26 will thus form one poleand the tool base material the other pole. For this reason, there isprovided a further contact plate 29 which has direct electrical contactwith the base material 21 of the tool and which is intended to abut afurther contact device 79 in the tool holder TH. Naturally, the contactplates 26, 29 are not covered by the electrically insulating protectivewear layer.

Electric conductors 80 from the contact devices in the tool holderextend to a signal processor 82. The signal processor itself has nobearing on the invention per se and will there-fore only be described inbrief.

The signal processor, which may be of any known kind, such as a purposeprogrammed computer, is constructed to determine the temperatureestablished by each thermocouple 10-13, with the aid of suitablesoftware. The processor is also programmed to calculate the distributionof temperature in the tool, at least at the cutting edge of the tooland/or at the near vicinity of the edge.

The processor is also constructed to detect and register abrupt changesin voltage from the thermocouples. For example, when wear on the tool issuch that the chamfer wear face has been worn down to the A--A in FIG.2, the thermocouples 10 and 11 will have been worn away in the process.The wearing away or obliteration of a thermocouple is registered as anabrupt change in the voltage associated with the thermocouple. In thisway, the processor will obtain information relating to the temperatureprevailing at different points on the cutting tool, the rate at whichthe tool is being worn and the extent of such wear. The wear rate can becalculated by registering when successive thermocouples are worn away.

Although the number of thermocouples provided can vary, it is believedthat from three to five thermocouples on the clearance or relief surfaceof the tool will suffice for the majority of applications.

Naturally, at least one thermocouple can be arranged in a similarfashion on the rake face 8 (see FIGS. 1 and 2) of the tool, at oradjacent the region where chip breaking takes place.

When the cutting tool concerned has two, three, four, six or eightcutting edges, the tool will be provided with thermocouples inaccordance with the aforegoing at each edge, in the same manner as thatdescribed above for an edge 3.

In the aforegoing there has been described an embodiment in which aconductor at one point forms a thermocouple with the base material ofthe cutting tool.

Second Embodiment

FIGS. 5 and 6 illustrate another embodiment in which each temperaturesensor comprises a point at which two electrical conductors of mutuallydissimilar materials and applied to the surface of the cutting tool areconnected together to form a thermocouple. The first of these materialsis designated 30-33 and the second is designated 34. The thermocouple isdesignated 35-38. The two materials may, for instance, be Pt and Pt/Rhor NiCr and NiAl. Extending from each thermocouple is a conductor whichleads to previously described contact plates 39, 40 corresponding to thecontact plates 26, 29 in FIG. 3.

As will be understood, it is also necessary with this second embodimentto coat the base material 21 of the tool with an electrically insulatingprotective layer 22 when the base material is electrically conductive.The conductors are also preferably provided with a protective wear layer25. FIG. 6 is a sectional view of a thermocouple configured inaccordance with the second embodiment.

Third Embodiment

FIG. 7 illustrates a third embodiment in which each temperature sensorcomprises a conductor 50-53 made of a material whose resistance changeswith temperature. The conductors 50-53 are also so placed as to be wornaway sequentially as the tool is worn in use. The conductors may, forinstance, be made of Ni or Pt. According to one preferred variant, theconductors 50-53 are placed parallel with and spaced from one anotherand at mutually different distances from the cutting edge on the chipbreaking side of the cutting tool. The conductors 50-53 are electricallyconnected in parallel to electrical conductors 54-55 whose respectiveresistances are not changed appreciably with changes in temperature,these last mentioned conductors 54, 55 extending from the ends of themutually parallel conductors to contact plates 56, 57 which correspondto the earlier mentioned contact plates 26, 29 and 39, 40.

The conductors 50-55 are placed on an insulating layer on the basematerial 21, when the base material is electrically conductive. Theconductors are also conveniently coated with a protective wear layer 25.

FIG. 8 illustrates the chamfer wear surface of a triangular indexablecutting insert 60. In the case of this embodiment, three thermocouples61-63 are mounted in accordance with the technique described above withreference to FIGS. 2 and 4. Conductors 64-66 extend from thethermocouples 61-63 to contact plates 67-69. The contact platecorresponding to the contact plate 29 of the FIG. 2 embodiment, i.e. thedirect contact to the base material is judiciously located in the centrehole 70 of the insert 60.

It will be obvious that the present invention enables an effective andadaptive control to be achieved, as mentioned in the aforegoing.

It will also be evident that the sensors can be positioned differentlyand in different patterns than exemplified above. The contact plates mayalso be placed at other locations.

The invention is therefore not limited to the above exemplifyingembodiments, since modifications and variations can be made within thescope of the following claims.

We claim:
 1. A cutting tool having at least one cutting edge (3), a rakeface (8) and a clearance surface (28) adjacent and associated with eachsaid at least one cutting edge, said tool being equipped with a toolstate indicator which comprises temperature sensors and electricalconductors applied to said tool, and wherein two or more saidtemperature sensors (10-13; 35-38; 50-53; 62-64) are placed on theclearance surface (28) of the tool (1) at mutually different distancesfrom said tool cutting edge (3), so that the temperature distribution inthe tool (1), at least at said cutting edge (3) thereof and in theimmediate vicinity of said cutting edge, can be calculated from electricsignals transmitted by said temperature sensors (10-13; 35-38; 50-53;62-64); and in that at least some of said temperature sensors on theclearance surface of said tool are so placed that one or more of thesensors on said clearance surface will be worn away in a successiveorder as the cutting edge and adjacent clearance surface of the tool (1)wears.
 2. A tool according to claim 1, wherein each said temperaturesensor (10-13; 35-38) is a thermoelement.
 3. A tool according to claim 1wherein said tool (1) is made of an electrically conductive hardmetalmaterial, said tool (1) is covered with an electrically insulating layer(22) at least on said clearance surface and said electrical conductorsare mounted on top of said layer.
 4. A tool according to claim 2,wherein each temperature sensor (35-38) consists of a point at which twoelectrical conductors (34; 30-33) placed on the tool and made ofmutually different materials are connected together and form athermocouple.
 5. A tool according to claim 2, in which said tool (1) ismade of an electrically conductive metal base material and is providedwith an electrically insulating material layer (22) at least on theclearance surface of said tool, and wherein one of said conductors (20)is placed on said insulating layer (22) for each said temperature sensor(10-13; 62-64); and in that said insulating layer (22) has formedtherein a hole (23) in which one end (24) of each of said conductors(20) is brought into contact with said base material (21) such as toform a thermocouple together with said base material (21) of the tool(1) and said thermocouple is said temperature sensor.
 6. A toolaccording to claim 1, wherein contact plates (26, 29, 39; 40; 67-70) areprovided on the tool and insulated from the tool, and each saidtemperature sensor (10-13; 35-38; 62-64) is connected electrically to anassociated one of said contact plates on the tool (1), and said contactplates are adapted to co-act with contact devices for the transmissionof electric signals from the tool (1) to a signal processor.
 7. A toolaccording to claim 1, wherein each said temperature sensor includes atemperature responsive conductor (50-53) which is made of a materialwhose electrical resistance changes with temperature.
 8. A toolaccording to claim 7, wherein said temperature responsive conductors(50-53) are placed in mutually parallel spaced apart relationship; andin that said temperature responsive conductors are connectedelectrically in parallel to said electrical conductors (54, 55) whichextend from said parallel temperature responsive conductors to contactplates (56, 57) on the tool, said contact plates (56, 57) being adaptedto co-act with contact devices for the transmission of electric signalsfrom the temperature sensors on the tool (1) to a signal processor.
 9. Atool according to claim 1, wherein at least one temperature sensor isplaced on the rake face (8) of the tool.